Nutritional strategies play an important role in facilitating peak athletic performances and research has shown that a state of physiological ketosis, from either a ketogenic diet or ketone supplementation, may have several benefits for athletes. These ergogenic properties may stem from the thermodynamic advantages ketones possess over other energy substrates as well as their ability to preserve glucose stores. Physiological ketosis has also shown improvements in cognitive performance, particularly for those suffering from neurological disease. The following thesis uses an oral ketone supplement (sodium- and potassium-based β-hydroxybutyrate) to elevate blood ketone concentrations to assess the effects of supplement induced ketosis on exercise metabolism and cycling performance (study 1, Chapter 2), as well as its effect on cognitive performance in an active population (study two, Chapter 3). As part of study 1, Twelve participants took part in a double-blind, placebo-controlled, randomised crossover design. The research assessed the effect of supplement-induced ketosis on 4 minute all-out cycling performance which followed 90 minutes at second ventilatory threshold (VT2). Upon ingestion of a ketone supplement (KET: 30 ml of Ketoforce; Prototype Nutrition, IL, USA) or placebo (PLA: 3g table salt; NaCl), effect size (ES) analysis, revealed an unclear 2.3 ±4.8% (Δ mean ±90% Confidence Interval (CI)) change in power output during a 4-minute maximal cycling performance test (4PT) in the KET trial compared to PLA. Therefore no substantial performance outcomes came as a result of ketone supplementation despite a three-fold increase in blood β-hydroxybutyrate concentration (ES ±90% CI= 3.02 ±0.8; very large) which was accompanied by a 2.2 ±1.9% increase in the respiratory exchange ratio (RER) during the submaximal exercise phase (ES = 0.51 ±0.4; moderate). During the 4PT increases in both VO2 (2.4 ±3.3%; ES = 0.24 ±0.3; small) and RER (4.3 ±3.3; ES = 0.75 ±0.5, moderate) were evident during the KET trial compared to the PLA. Similarly in study 2, the effects of oral ketone supplementation on cognitive function were assessed. Using a single blind, placebo-controlled design cognitive function was evaluated through five tests intended to assess different components of neuro-muscular performance, reaction time, processing speed and memory recall: finger tap test (FTT), stroop test (ST), reaction time test (RT), monkey-ladder test (MLT) and one-card test (OCT). The reliability of each test was also assessed using a test-retest protocol. No statistically significant differences (p > 0.05) were observed in cognitive function between groups. ES analysis revealed small improvements in the KET trial for ST (ES = 0.34 ±0.4) as well as the MLT (ES = 0.34 ±0.4) with either trivial or unclear results for FTT, RT and OCT when compared to PLA. In conclusion, ingestion of an oral ketone supplement was shown to have no substantial impact on human performance as measured through 4-minute cycling performance and measures of cognitive function.